Coefficient of Linear Expansion
Name: ____________________
Class: _____________________
Pre-Lab Questions Page
Roster#____________________
Instructor:___________________
1. What is the symbolic representation for the coefficient of thermal linear expansion and
its unit?
symbol = __________________
unit:__________________
2. A 10.0 cm french-fry temperature changes by 37oC. If the final length of the fry is
50.03 cm, calculate the coefficient of thermal linear expansion of the fry.
3. Why are gaps or spaces placed between cement sidewalks, instead of laying them so
that each side touch?
4. What is the coefficient of thermal linear expansion for the following materials:
aluminum = αAl =________________
brass = αbr = ____________________
steel = αst = _________________
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Name: __________________________
Date of Lab:______________________
Lab Partners:______________________
______________________
Roster#_______________
______________________________________________________
Coefficient of Linear Expansion
OBJECTIVE: The purpose of this lab is to measure the coefficient of thermal linear
expansion for a selection of metals and compare the results to the theoretical values.
APPARATUS:
Coefficient of linear expansion apparatus
Boiler and plastic tubing
Centigrade thermometer
Meter stick
Two metal rods
Paper towels and pot holders
Cup to catch run off
Figure 1: Linear Expansion apparatus
INTRODUCTION: Almost all matter expands when it is heated. A solid of
cylindrical cross-section where the length is by far the largest dimension will expand
according to the law;
∆L = Loα∆T
equation 1.
where;
∆L is the change in length,
L0 is the initial length,
α is the coefficient of linear thermal expansion for various materials,
∆T is the change in temperature.
The theoretical value for the coefficient of linear expansion for various substances is
given in your textbook.
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PROCEDURE:
1.
Using the hot plate, heat the water to boiling. While the water is being heated work
on the rest of the procedures.
2. Using a meter stick, measure the initial length of the steel rod at room temperature.
Avoid excessive handling of the rod because your body will transfer heat into the rod,
causing it to expand. Record the initial length in centimeters.
3. Record the room temperature on your data sheet, this is the initial temperature of the
rod.
4. Assemble the apparatus. Insert the rod into the metal jacket. Hold the rod by its ends
to avoid heating it. Align the dial pin with the metal rod. Do not attach the plastic
tubing from the boiler yet.
5. Record the initial reading of the gauge. The gauge reads in inches and each division
on the gauge is 0.001 inch.
6. Insert the thermometer into the hole in the center of the metal jacket. Attach the hose
from the boiler to the metal jacket. Allow steam to pass through the apparatus until
the internal temperature stabilizes to about 100 oC, due to energy loses you probably
will not be able to get to 100 degrees. Allow steam to pass through the system for
five minutes and observe the expansion of the rod on the gauge by checking the
reading every two minutes. Observe and record the final gauge reading. The change
in length of the rod is the difference between the final gauge reading and the initial
gauge reading. Be sure to convert your units from inches to centimeters.
7. Using a potholder (insulated glove), remove the plastic tubing and tilt the apparatus to
drain the hot water. Be very careful, steam DOES burn skin!! The whole
apparatus is HOT!! Cool the steam shield in the sink to prepare for the next
measurement.
8. For the second measurement repeat the previous steps using the brass, copper or steel
rod.
DATA: Construct a data table that looks like this.
Steel
Aluminum
Brass
Copper
Initial length of the rod (Lo)
Initial micrometer setting
Final micrometer setting
Change in Length (∆L)
Initial temperature
Final Temperature
Change in temperature (∆T)
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CALCULATIONS/ANALYSIS:
1. Use equation 1 to determine the coefficient of linear expansion for each of the (2) rods
that were used during the experiment.
2. Compute the percent error between your experimental value and the theoretical value
of the coefficient of linear expansion found in the textbook using the following equation:
% error =
Theoretical − Experimental
Theoretical
x 100
Make a table of your results like the one below.
Steel
Brass
Aluminum
Copper
Experimental Coefficient of Linear
Expansion (α)
Theoretical value of the coefficient
(from the book)
Percent Error
QUESTIONS:
1. What is the relationship between the coefficient of thermal linear expansion and the
change in length?
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2. According the coefficient of thermal linear expansion, which of the two rods used in
the experiment would you expect to have the greatest expansion, if all other things are
equal? Did your experimental results verify your theory?
3. What role does the temperature range in a certain area of the country and the
coefficient of thermal linear expansion play in selecting materials used in
construction of bridges, houses, etc?
4. A 5.0 m rod is heated from 23oC to 35oC in which the length of the rod change by 7.2
x 10-4 m, what is the rod made of? Hint: determine its coefficient of thermal linear
expansion.
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